Regulation of the immune response is an important factor in the ability of animal to protect itself against enviromental antigens. While the response itself has been described in some detail, several aspects of its control are poorly understood. We wish to investigate the DNA splicing mechanism by which immunoglobulin variable region genes are assembled, an essential part of the generation of immunoglobulin diversity. An in vitro system capable of splicing V and J genes will be developed, using a specially engineered lambda phage as the splicing template. In this way the splicing mechanism may be completely characterized and the splicing enzyme (s) identified.